Astrophysics

=Astrophysics=

**The solar system and beyond**
**E.1.1 Outline the general structure of the solar system.**
 * The solar system has 8 planets orbiting the sun in ellipses motions, and moon orbiting the planets.
 * Order of planets
 * By distance: Mercury < Venus < Earth < Mars < (asteroid field) < Jupiter < Saturn < Uranus < Neptune.
 * By size: Mercury < Mars < Venus < Earth < Neptune < Uranus < Saturn < Jupiter.
 * __Comets__: mixtures of rock and ice in very elliptical orbits around the Sun. Their 'tails' always point away from the Sun.
 * Asteroid belt: many asteroid orbit around the Sun between Mars and Jupiter in a placed called the asteroid belt.
 * __Meteoroid__: An asteroid on a collision course with another planet
 * __Meteor:__ meteoroid that enter's and burns in the Earth's atmosphere
 * __Meteorites__: meteors that land on earth

**E.1.2 Distinguish between a stellar cluster and a constellation.**


 * **Stellar Clusters:** **group of stars**
 * Stars group into stellar clusters due to the attraction of gravity.
 * Stellar clusters are close together. (There may be thousands of stars in a group)
 * **Constellation: patterns of stars**
 * From Earth stars in a constellation appear close to each other, while they can be very far apart.

**E.1.3 Define the //light year//.**
 * A light year is the distance it takes for light to travel for a year. 1 ly = (3.0 x 10^8 m/s) x (3.1536 x 10^7 s/yr) = 9.46 x 10^15 m.

**E.1.4 Compare the relative distances between stars within a galaxy and between galaxies, in terms of order of magnitude.**


 * Distance between.
 * Stars within a galaxy: ~ 10^17 m
 * Galaxies within a cluster: ~ 10^23 m
 * Galaxies clusters: ~ 10^24 m

**E.1.5 Describe the apparent motion of the stars/constellations over a period of night and over a period of a year, and explain these observations in terms of the rotation and revolution of the Earth.**


 * Over a period of a night
 * the constellations appear to rotate across the sky/rotate around one star (Polaris). This apparent rotation is a result of the rotation of the Earth about its own axis.
 * Over a period of a year
 * stars and constellation slowly change in appearance/position. This variation over the period of one year is due to the rotation of the Earth about the Sun.

**E2**
**Energy Source**
 * E.2.1 State that fusion is the main energy source of stars. **
 * Fusion, particularly Hydrogen fusion into Helium, is the main energy source of stars.j
 * As the mass of the products is less than the mass of the reactants, energy is released during the fusion process. It can be calculated by E=mc^2


 * E.2.2 Explain that, in a stable star (for example, our Sun), there is an equilibrium between radiation pressure and gravitational pressure. **
 * Outward radiation pressure produced from the fusion reactions counteract the inward gravitational force.
 * As long as the two forces are at equilibrium, the stars is stable.
 * Luminosity **
 * E.2.3 Define the //luminosity// of a star. **
 * Luminosity is the total power radiated by a star. That is also the amount of energy radiated per second.
 * L =σAT^4 (where σ is the Stefan-Boltzmann constant 5.67 x 10^-8 W m^-2 K^-4)
 * Factors that affect luminosity are ____ of the star
 * 1. surface area
 * 2. surface temperature

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 * E.2.4 Define //apparent brightness// and state how it is measured. **
 * Apparent brightness of a star is the power received per unit area, as observed from earth.
 * b = L / A
 * b = L / (4πr^2) The brightness is inversely proportional to the distance.
 * Wien's Law and the Stefan-Boltzmann Law **
 * E.2.5 Apply the Stefan–Boltzmann law to compare the luminosities of different stars. **
 * L =σAT^4 (where σ is the Stefan-Boltzmann constant 5.67 x 10^-8 W m^-2 K^-4)
 * Power is dependent on the surface area and temperature of the star.
 * Apparent Brightness can be calculated by
 * b = σAT^4 /(4πr^2)
 * L- actual luminosity of the star
 * b - apparent brightness from observer


 * E.2.6 State Wien’s (displacement) law and apply it to explain the connection between the colour and temperature of stars. **


 * Stellar Spectra **
 * E.2.7 Explain how atomic spectra may be used to deduce chemical and physical data for stars. **
 * E.2.8 **
 * Describe the overall classification system of spectral classes. **


 * Types of Star **
 * E.2.9 Describe the different types of star. **
 * E.2.10 Discuss the characteristic of spectroscopic and eclipsing binary stars. **


 * The Hertzsprung-Russel diagram (HR diagram) **
 * E.2.11 Identify the general regions of star types on a Hertzsprung-Russell (HR) diagram. **